Control apparatus



Jan. 5, 1943. J FLUKE 2,307,580

CONTROL APPARATUS Filed Aug. 29, 1941 Ihvenb or: John M. Flu ke,

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HIZLYALL 0T n ABC Patented Jan. 5, 1943 CONTROL APPARATUS John M. Fluke, Arlington, Va., assignor to Gener- 0.1 Electric Company, a corporation of New York Application August 29, 1941, Serial No. 408,887

8 Claims.

My invention relates to control apparatus and particularly to electronic apparatus for timing and sequencing a plurality of operations.

It is an object of my invention to provide a control in which a voltage whose magnitude varies with the lapse of time sequentially operates a plurality of electric discharge devices according to a time pattern determined by different bias voltages which oppose the effect of said timing voltage on the control elements of said electric discharge devices.

It is also an object of my invention to provide electronic control apparatus in which the timing of one operation may be adjusted without materially altering the timing sequence of other operations or the timing of such other operations.

Further objects of my invention will become apparent from a consideration of the system diagrammatically represented in Fig. 1 of the accompanying drawing for operating a plurality of load devices. Fig. 2 of this drawing is a diagram which will be used in explaining the operation of this system.

In accordance with my invention a plurality of circuits, each of which includes an electric discharge device having a control element, is employed for controlling the energization of a plurality of load devices. The operations of these devices are timed to follow one another in a desired sequence. The timing and sequencing of these operations are determined by applying difierent bias voltages to the control elements of these electric discharge devices and simultaneously opposing these bias voltages with a voltage whose magnitude varies with the lapse of time. Means are also provided for simultaneously varying these bias voltages for determining the time during which one of said electric discharge devices functions without materially altering the timing sequence or timing operations determined by the other electric discharge devices.

In the system of Fig. 1 of the drawing, my control has been used to time the flow of welding current, then operate a cutting device, and finally operate a feeding mechanism in accordance with a preset time pattern.

The electrodes l0 and H and the cutting mechanism I2 of the resistance welding machine diagrammatically illustrated have been described and claimed in my United States Letters Patent 2,263,294, granted November 18, 1941, and assigned to the assignee of this invention. Electrode Ii is carried by a support member l3 mounted on a rod H which is clamped in the lower arm l5 of the welding machine. Electrode I0 is carried by the upper arm iii of the welding machine. This arm projects from a slide H5 which is moved toward and away from arm l5 by a toggle IIB, one end of which is connected to slide H5 and the other end of which is connected to a piston rod l'l. This piston rod is held against a stop i8 by air pressure acting on its piston within a cylinder i9. Air at a predetermined pressure is supplied through a pipe 20 to the upper part of cylinder l5 and determines the welding pressure between electrods Ill and II when toggle H6 has been straightened sufiiciently to move piston rod H from stop I8.

Toggle H6 is collapsed and straightened by an arm 2| which is connected to an eccentric strap 22. This eccentric strap rides on an eccentric 23 which is mounted on a shaft 24 and rotated therewith by a substantially constant speed motor 25. A switch cam 26 is also mounted on shaft 24 and is oriented relative to eccentric 23 so that when the eccentric is in a position to straighten toggle I I6 sufficiently to apply welding pressure to electrodes l0 and II, this switch cam moves a member 21 of a switch 28 to bring contacts 29 and 30 of this switch into engagement with one another.,- The arrangement is also such that when the welding pressure is released by the eccentric 23 acting to collapse toggle H6, switch member 21 moves to a position completing a circuit between contacts 29 and 3| of switch 28.

A measured length of material 32 used in making the welded assembly is fed by ahitch feed 33 through a passageway in the cutting cylinder 34 of the cutting mechanism I2. Hitch feed 33 and cutting mechanism l2 are mounted on support l3 for electrode H. Cutting cylinder 34 is provided with an arm 35 which is biased by a spring 36 to a position permitting this feeding operation. It may be moved against the bias of spring 36 through the agency of electromagnet 31 to rotate cylinder 34 relative to electrode l I and cut the measured length of material extending from cylinder 34.

The hitch feed is operated by an electromagnet 38. This electromagnet moves an arm 39 against the bias of springs 40 and M to move a slide 42 relative to its support 43. Slide 42 and its support 43 are provided with ratchets 44 and 45 which engage and cooperate in feeding material 32. The hitch feed is cocked by the energization of electromagnet 38 and when this electromagnet is deenergized spring 4i moves slide 42 forwardly carrying along material 32 due to the engagement of ratchet 44 therewith.

Welding current is supplied to electrodes I8 and II by a welding transformer 46. The terminals of the secondary 41 of this transformer are connected to electrodes I8 and II of the welding machine and the terminals of its primary 48 are connected to a source of alternating current 49 through reversely connected electric discharge devices 58 and The conductivity of electric discharge devices 58 and 5| is controlled by electric discharge devices 52 and 53 associated therewith. The operation of electromagnet 31 for cutting mechanism I2 is determined by a full-wave controlled rectifier 54 which in turn is controlled by electric discharge devices 55 and 58 acting through the agency of an electric discharge device 51. The operation of electromagnet 38 for operating the hitch feed 33 is determined by a full-wave controlled rectifier 58 which in turn is controlled by an electric discharge device 59. The sequential operations of electric discharge devices 52, 55, 53 and 59 time the welding operation, thereafter sever an end portion of material 32, and then operate the feeding mechanism 33 to supply a measured length of material 32 for the next welding operation.

Electric discharge device 52 serves the dual purpose of timing as well as controlling electric discharge device 58. It connects through its anode-cathode circuit the anode of electric discharge device 58 to its control element 19.

Control element 68 of electric discharge device 52 is connected to a slider 5| on a resistor 82. This resistor is connected between resistors 53 and 54 across a source of direct current 55, 33. This source of direct currentris obtained from an alternating current source through a rectifier 51 which is connected so that conductors 55 and 66 become respectively positive and negative conductors.

The cathode of an electric discharge device 93 is connected between resistor 52 and resistor 84 above referred to. The anode of this electric discharge device is connected through contacts 29 and38 of switch 28 and loading resistor 14 which is in parallel with a charging resistor 15 and timing condenser 18, to the positive conductor 85 of the direct current source of supply 55, 65. A discharge resistor 18 is connected across condenser 15 through contacts 29 and 3| of switch 28.

Electric discharge device 68 causes the flow of welding current to start at the desired point on the voltage wave of source 49 after contacts 29 and 38 of switch 28 have closed. The control element 59 thereof is connected to the negative terminal of resistor 64 through the secondary 18 of a peaking transformer 1| which supplies a voltage overcoming the negative bias obtained from resistor 64. The point on the alternating current wave of the source of supply 49 for the welding transformer 46 at which this peaked voltage occurs is controlled'by the variable resistor 12 connected-in series with one of the primary windings 13 of transformer 1| which is energized from the alternating current source 49.

As previously stated, control element 58 of electric discharge device 52 is connected to slider II of resistance 62. Its cathode is connected at 11 between charging resistor 15 and condenser 15.

Electric discharge device 53 controls electric discharge device 5|. It connects through its anode-cathode circuit the anode of electric discharge device ,5I to its control element 88. A

asoasso bias voltage 188 out of phase with the anode voltage of electric discharge device 53 is applied to its control element 8| through a transformer 92 which is energized from source 49. A selfrectified bias voltage is also applied to this control element by the parallel connected resistor and condenser 83. A control voltage for rendering electric discharge device 53 conductive is obtained from a feedback transformer 84 whose secondary is connected in circuit with control element 88 of electric discharge device 53 and whose primary is connected across the primary 43 of welding transformer 48.

Control elements 85 and 86 of electric discharge devices 55 and 58 are connected to point 11 between charging resistor 15 and timing condenser 18. The cathodes of these electric discharge devices are connected respectively through bias voltage condensers 81 and 88 to slider 8| on resistor 82. The voltage of condenser 88 is ad- Justed to be greater than the voltage of condenser 81. This is accomplished by an adjustment of sliders 89 and 98 on resistors 9| and 92. These resistors 9| and 92 are connected in parallel with one another and in series with resistor 93 across the output terminals of rectifier 94. These resistors serve as a source of direct current voltage for electric discharge devices 55 and 56. The anode of electric discharge device 55 is connected through resistors 95 and 96 to the positive terminal of resistor 93 and the cathode of electric discharge device 55 is connected to slider 89'on resistor 9|. The anode of electric discharge device 55 is connected through resistors 91 and 93 to the positive terminal of resistor 33 and its cathode is connected to slider 98 on resistor 92.

When electric discharge device 55 becomes conductive it causes electric discharge device 5:? to become conductive and when electric discharge device 58 becomes conductive it causes electric discharge device 51 to become nonconductiw. The control element 99 of electric discharge device 51 is connected to a slider I88 on resistor 91 and its cathodeis connected through 9. ate. bilizer consisting of a parallel connected resistor and condenser I8I, to slider I82 on resistor 99. The anode cathode circuit of electric discharge device 51 is connected across a resistor I83 through a resistor I84. Resistor I83 in turn is connected across the output teminals of a full-wave rectifier I85 50 that it serves as a source of direct current voltage.

long as electric discharge device 51 is conductive it causes the controlled full-wave rectifier 54 to become conductive and energize electromagnet 31 of the cutting mechanism. A source of negative bias voltage for control elements I of the electric discharge devices of rectifier 54 is obtained from the secondary I81 of a bias transformer and slider I88 on resistor I83. The control voltage for these electric discharge devices is obtained from resistor I84 through its slider I89. The output circuit of rectifier 54 is connected to the operating winding of electromagnet 31 whichis provided with a smoothing condenser II 8,

The electric discharge device 59 controls the operation of electromagnet 38. Its control element III is connected to a slider 2 on a resistor II3 which is connected across a portion of resistor 83. Its cathode is connected through a stabilizer consisting of a p rallel connected resistor and condenser II4, to point 11 between charging resistor 15 and timins condenser 19.

Its anode cathode circuit is completed through a resistor 2|5 to the terminals of a resistor 2|6. This resistor is connected across the output circuit of a rectifier Ill and consequently serves as a source of direct current voltage for electric discharge device 59. I

When electric discharge device 59 is conductive full-wave rectifier 58 also becomes conductive to energize electromagnet 38 of the hitch feed 33. The operating winding of electromagnet 38 is also provided with a smoothing condenser 8. A source of negative bias voltage for control elements 9 of the electric discharge devices of rectifier 58 is obtained from the secondary |28 of a bias transformer and terminal |2| of resistor 2|6. The control voltage for these electric discharge devices is obtained from resistor 2|5 through its slider I22.

Electric discharge devices 55, 56, 51, and 58 may be of the vacuum type in which the control elements above identified are control grids. These electric discharge devices are also provided as indicated with suppressors and screen grids. As usual, the suppressor grid of each electric discharge device has been connected to its cathode and its screen grid has been connected to .a source of voltage that is positive relative to its cathode. Discharge devices 58, 5|, 52, 53, and 68 and the electric discharge devices of fullwave rectifiers 54 and 58 are of the gaseous type. The output circuit of each of the rectifiers 6?, 94, I85, and H1 is provided with a filter circuit including a series connected inductance and a parallel connected condenser.

In order to simplify the drawing only the secondaries of certain alternating current transformers have been. illustrated in the drawing. It is to be understood, of course, that each of these secondaries is energized through a primary which is connected to a source of alternating current which may be the same source 49 to which the welding transformer 48 is connected.

The system has been shown in its deenergized condition. None of the controlled electric discharge devices is conducting. The alternating current source is applied to the anode-cathode circuits of the electric discharge devices connected thereto and to the input circuits of the rectifiers and their filaments as well as the oathode heaters of the electric discharge devices. By

reason of the energization of the rectifiers, the

several sources of direct current control voltage across the potentiometers or resistors connected thereto will be available.

The system is set in operation by starting motor 25. Rotation of this motor rotates eccentric 23 which through its strap 22 and arm 2| straightens toggle I It to move electrode I8 toward electrode I|. As a result of this movement electrode I0 engages the assembly to-be welded including the end of material 32 extending through cutting cylinder 34. The assembly may comprise a switch member to which a contact formed from material 32 is welded. The switch member will be located on electrode between it and the end of material 32 extending through cutting cylinder 34. Thereafter further straightening of toggle ||8 moves piston rod upwardly against the air pressure in cylinder I9 to apply a welding pressure determined by the amount of this air pressure. About this time switch cam 25 moves switch member 21 to bring switch contacts 29 and 38 into engagement with one another.

When contacts 29 and 38 of control switch 28 engage one another a charging circuit for condenser I8 is completed from conductor 55 through resistor 15 and electric discharge device 68 to conductor 58. Electric discharge device 68 is normally held nonconductive by the negative bias applied to its control element 63 and consequently the engagement of contacts 29 and 38 does not initiate the flow of charging current to condenser 16. At some point in the positive half cycle of the alternating current source determined by the adjustment of variable resistor 12, peaking transformer 1| applies a voltage to control element 89 of electric discharge device 88 which overcomes this negative bias and renders electric discharge device 88 conducting. Since the voltage on the anode of this electric discharge device is direct current this tube will remain conducting until its anode circuit is opened by the separation of contacts 29 and 38 of control switch 28.

When contacts 29 and 33 of control switch 28 are closed and electric discharge device 88 becomes conductive point 11 between charging resistor i5 and timing condenser 16 is brought to the potential of conductor 66 except for the voltage drop in resistor 64 and about 15 volts drop in electric discharge device 68. It is to be noted that point I1 is connected to the cathode of electric discharge device 52 whose control element 68 is connected to a more positive source of potential determined by the connection of slider 6| with resistor 62 of potentiometer 63, 82, 64. Electric discharge device '52 will consequently become conductive and in turn causes electric d scharge device 58 to become conducting, The welding transformer 48 will consequently become energized from the source of supply 49.

The half cycle energization of the welding transformer through electric discharge device 58 will energize the control or feedback transformer 84 which will overcome the alternating bias voltage of transformer 82 and the self-rectified bias voltage of 83 to render electric discharge device 53 conductive which in turn renders electric discharge device 5| conducting during the next half cycle. Electric discharge device 58 will continue to conduct until the current passes through zero, at which time, due to the inductive nature of the welding transformer load, there will be considerable voltage across electric discharge devices 5| and 53 for the above described operation.

At the same time electric discharge device 52 became conducting electric discharge device 59 also became conducting energizing through controlled rectifier 58 the electromagnet 33 of hitch feed 33. The energization of electromagnet 38 cooks the hitch feed against the bias of its spring 4| so that upon deenergization of electromagnet 38 the hitch feed will supply a new length of material 32 for the next welded assembly.

Electric discharge device 59 becomes conductive by reason of the positive bias voltage applied to its control element I through potentiometer 3. The cathode of electric discharge device 59 is connected through stabilizer ||4 to point ll which is negative relative to the bias voltage applied to its control element When electric discharge device 59 becomes conducting current flows from the plus terminal of resistor 2|6 through resistance 2|5 and stabilizer M4 to the negative terminal of 2 6. The voltage drop across the lower portion of resistor 2|5 overcomes the bias voltage obtained between the positive terminal and slider |2| of resistor 2|6 and the alternating bias of transformer secondary I20,

14 connected across charging resistor 15 and condenser 16 will draw sufiicient current to keep electric discharge device 88 ionized after condenser 15 has been fully charged.

At a time determined by the setting of slider 6| on resistor 52 a negative voltage will be applied to control element 58 of electric discharge device 52, thereby rendering it nonconductive after its anode voltage reverses and the current therethrough falls to zero. Consequently electric discharge devices 50, 53, and also become non-conductive and interrupt the flow of welding current.

At some later time determined by the bias voltage of condenserv81 electric discharge device 55 will become conductive. It will be noted that the control element 85 of this electric discharge device is connected to point 11 which is growing positive due to the charging of condenser and that its cathode is connected through the bias voltage of condenser 81 to slider 5| of resistor 62.

At a stilllater time electric discharge device 56 will become conducting. It is to be noted that its control element 86 is also connected to point 11 which is growing positive as condenser Hi is being charged and that its cathode is connected throughthe bias voltage of condenser 88, which is greater than the bias voltage of condenser 81, to slider 6| of resistor 62. I

When electric discharge device 55 becomes conducting it connects resistors 96 and 95 across resistor 93 and a portion of resistor 9|. A voltage drop consequently appears across resistor 95 which makes control element 99 of electric discharge device 51 positive relative to its cathode. This device consequently becomes conducting and in like manner previously described for electric discharge device 59 and renders controlled rectifier 54 conducting to energize the electromagnet 31 of the cutting mechanism and sever strip 32 from the welded assembly.

When electric discharge device 55 becomes conducting, it connects resistors 91 and 98 across resistor 93 and a portion of resistor 92. A voltage drop consequently appears across resistor 91 which makes control element 99 of electric discharge device 51 negative relative to its cathode. Electric discharge device 51 consequently becomes nonconducting, causing controlled rectifier 54 to be nonconducting and thereby deenergizing electromagnet 31. Upon the deenergiz'ation of electromagnet 31 the cutting mechanism is returned to the position illustrated so that a new length of material 32 may be fed through and between electrodes I8 and H.

During the cutting operation electrodes l8 and I l engage and hold the welded assembly. Thereafter motor begins to raise electrode ID from the welded assembly but before switch cam 25 separates contacts 29 and 38 of switch 28 sufilcient time elapses for point 11 to become sufliciently positive to deenergize electric discharge device 59 and consequently electromagnet 38. The hitch feed which has been previously cocked now moves a new length of material 32 into position over electrode H for the next welding operation. Shortly thereafter contacts 29 and 3| of switch 28 are closed discharging condenser 18 through resistor 18 and thereby conditioning the timing circuit for the next sequence of operations which will be a repetition of those above described. These operations continue until motor 25 is stopped.

The above operation may be summarized by referring to Fig. 2 which diagrammatically represents the increase in voltage of point 11 with the lapse of time, an adjustment of slider 5| for applying a bias voltage of 150 volts in the control circuit of electric discharge device 52, an adjustment of slider 89 for increasing this bias voltage by 19 volts in the control circuit of electric discharge device 55, an adjustment of slider 90 for increasing this first mentioned bias voltage by 48 volts in the control circuit of electric discharge device 56, and an adjustment of slider N2 of potentiometer 3 for applying a bias voltage of 290 volts in the control circuit of electric discharge device 59. Welding current flows from 0 time when contacts 29 and 30 of switch 28close and electric discharge device 68 becomes conductive until time A when the voltage of point 11 equals the voltage of slider 6|. At time B when the additional 19 volts of condenser 81 are attained by Point 11 electric discharge device 55 becomes conductive to energize electromagnet 31 which energizes the cutting mechanism. At time C when the additional 48 volts of condenser 88 are attained by point 11, electric discharge device 55 becomes conducting to deenergize electromagnet 31. It will be noted that the energization and deenergization of electromagnet 31 occurs in a time sequence determined by the bias voltages across condensers 81 and 88 which are always greater by a predetermined amount than. the adjustable bias voltage obtained by adjusting slider 6| on variable resistor 62. By individually adjusting the bias voltages of condensers 81 and 88 through the agency of sliders 89 and 98 it is possible to time the energization and deenergizatioii of electromagnet 31 relative to the time welding current ceases flowing. Electric discharge device 59 causes electromagnet 38 to be energized at zero time and to be deenergized at time D when the voltage of point 11 equals 290 volts which is subsequent to the operation of the cuttingsmechanism under the control of electromagnet It is of course apparent that my control system may be variously modified without departing from my invention. In place of condenser 16, other energy storage devices may be employed for obtaining a timing voltage. Furthermore, some of the electric discharge devices may be set to have initially a slight conduction, rat-her than zero conduction as stated above. Thus, for example,

electric discharge devices 51 and 59 may be set for a slight conduction before the system is set in operation by the closure of contacts 29 and v 38 of switch 28. Types of electric discharge devices difier ent from those above described, yet functionally the equivalent thereof, may be used. Furthermore, in order to simplify the description of the system illustrated it has been assumed that the various electric discharge devices become conducting when their control elements are posi tive relative to their cathodes. It is of course apparent that this is not always the case and that allowance must be made therefor when electric discharge devices having different characteristics are employed.

In view of the above described application of my invention modifications, variations and other applications thereof will occur to those skilled in the art. I consequently intend in the appended claims to cover all such modifications, variations, and applications as fall within the true spirit and scope of my invention as defined in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Control apparatus comprising an electrical energy storage device, means for charging and discharging said energy storage device and thereby producing a timing voltage which varies in magnitude with the lapse of time, a plurality of electric discharge devices each or which has a control element, a plurality of circuits each of which includes one of said electric discharge devices, means ior applying a different bias voltage to the control element of each of said electric discharge devices, means for simultaneously adjusting all of said bias voltages by the same amount and thereby adjusting the time during which one of said biased voltages is effective against said timing voltage without materially altering the time required for said timing voltage to pass from one value of bias voltage to another, and means for simultaneously applying said timing voltage to each of said control elements 01' said electric discharge devices in opposition to said bias voltages and thereby controlling the conductivities of said electric discharge devices and the timing operation of one of said circuits without materially altering the timing sequence in which said circuits operate.

2. Control apparatus comprising a plurality of electric discharge devices'each of which has a control element, a plurality of circuits each of which includes one of said electric discharge devices, a condenser, means for charging and discharging said condenser and for producing a timing voltage which varies in magnitude with the lapse of time, means for simultaneously applying said timing voltage to each of said control elements of said electric discharge devices, means for timing the sequential operation of said electric discharge devices by applying to said control elements of said electric discharge devices in opposition to said timing voltage a bias voltage which is different for each of said electric discharge devices by an amount equal to the variation in said timing voltage for a desired time interval in said sequential operation of said electric discharge devices, and means for simultaneously adjusting said bias voltages by the same amount and thereby adjusting the operating time of that one of said electric discharge device having the low value of bias voltage applied thereto While maintaining said desired sequential operation of said electric discharge devices according to the time pattern determined by the diffrences in their said bias voltages.

3. Control apparatus comprising a source of direct current, a condenser, a resistance, a switch which in one position connects said condenser and said resistance in series with one another across said source of direct current to charge said condenser and in another position interrupts said charging circuit and completes a discharge circuit for said condenser, means including an electric discharge device for controlling the operation of a load device, means including another electric discharge device for controlling the operation of another load device, each of said electric discharge devices having a control element, a control circuit for each of said electric discharge devices, each of said control circuits having a common portion including an adjustable bias voltage which is opposed to and acts conjointlywith avoltage which varies in accordance with the charge on said condenser for adjusting the time interval before one of said electric discharge devices exerts a control on its said load device and each of said control circuits having a portion which is individual to-each of said control circuits, and means in the portions of said control circuits individual to each of said electric discharge devices for providing a predetermined difference in the bias voltages applied to the control elements of said electric discharge devices and thereby controlling the time interval between the control of one of said load devices by one of said electric discharge devices and the control of the other of said load devices by the other of said electric discharge devices.

4. Control apparatus comprising a source of direct current, a condenser, a resistance, a switch which in one position connects said condenser and said resistance in series with one another across said source of direct current to charge said condenser and in another position interrupts said charging circuit and completes a discharge circuit for said condenser, a source of alternating current, means for initiating the flow of direct current to said condenser at a predetermined point on the voltage wave of said source of alternating current, means including an electric discharge d v e fo n ng a load device from said source of alternating current so long as said electric discharge device is rendered conductive, means including another electric discharge device for controlling the operation of another load device, each of said electric discharge devices having a control element, a control circuit for each of said electric discharge devices, each of said control circuits having a common portion including an adjustable bias voltage which is opposed to and acts conJointly with a voltage which varies in accordance with the charge on said condenser for adjusting the time interval before one of said electric discharge devices exerts a control on its said load device and each of said control circuits having a portion which is individual to each oi! said control circuits, and means in the portions of said control circuits individual to each of said electric discharge devices for producing a predetermined difference in the bias voltages applied to the control elements of said electric discharge devices and thereby controlling the time interval between the control of one of said load devices by one of said electric discharge devices and the control of the other of said load devices by the other of said electric discharge devices.

5. Control apparatus comprising a source of direct current, a condenser, a resistance, a switch which in one position connects said condenser and said resistance in series with one another across said source of direct current to charge said condenser and in another position interrupts said charging circuit and completes a discharge circuit for said condenser, a control circuit including an electric discharge device having an anode, cathode, and control element, a second control circuit including a second electric discharge device having an anode, a cathode, and control element, means for connecting a source of bias voltage between the cathode of said second electric discharge device and the control element of said first electric discharge device, means for directly connecting the control element of said second electric discharge device to the cathode of said first mentioned electric discharge device and both said cathode of said first electric discharge device and said control element of said second electric discharge deviceto a voltage that varies in accordance with th charge and voltage of said condenser, and means for adjustably connecting the control element of said first electric discharge device and the cathode of said second electric discharge device in circuit with said source of bias voltage to a second source of bias voltage which is in circuit with said voltage that varies in accordance with the voltage of said condenser.

6. Control apparatus comprising a load device, means for controlling the electrical energization of said load device, said means including an electric discharge device having a control element, a second load device, means for electrically energizing said second load device, said means including a second electric discharge device having a con trol element, means for electrically deenergizing said second load device, said means including a third electric discharge device having a control element, means for applying a difierent bias voltage to the control element of each or said electric discharge devices to predetermine the sequential operation of said electric discharge devices,

the bias voltage applied to said second electric discharge device being greater than that applied to said first electric discharge device and the bias voltage applied to said third electric discharge device being greater than the bias voltage applied to said second electric discharge device, a condenser,

means for charging and discharging said condenser and producing a timing voltage which varies in magnitude with the passage of time, means for simultaneously applying said timing voltage to each of said control elements of said electric discharge devices in opposition to said bias Voltages for rendering said first electric discharge device conductive for a predetermined time interval and thereafter rendering said second and third electric discharge devices conductive in a predetermined sequence after predetermined time intervals determined by the difi'erences in the bias Voltages applied to said control elements of said electric discharge devices, and means for simultaneously adjusting all of said bias voltages by the same amount for adjusting the time during which said first electric discharge device is conductive while maintaining said timed sequential operation of said electric discharge devices in accordance with said predetermined differences in their bias voltages.

'7. Control apparatus comprising means including an electric discharge device for controlling the electrical energization of a load device so long as said electric discharge device is rendered conductive, means including a second electric discharge device for electrically energizing a second load device when said second electric discharge device is rendered conductive, means including a third electric discharge device for electrically deenergizing said second load device when said third electric discharge device is rendered conductive, each of said electric discharge devices being provided with a control element and acontrol circuit therefor, a condenser, means for charging and discharging said condenser and thereby producing a timing voltage which varies in magnitude with the lapse of time. means for initiating said timing voltage and simultaneously connecting it in each of said control circuits, means in each of said con trol circuits for applying to said control elements of said electric discharge devices bias voltages which are of increasingly greater magnitude for said second and third electric discharge devices in the order named from that applied to said control element of said first electric discharge device and which render said first electric discharge device conductive and said second and third electric discharge devices nonconductive at the time said control circuits for said electric discharge devices are completed by the connection of said timing voltage in said control circuits, and means for simultaneously adjusting said bias voltages of said first, second, and third electric discharge devices by the same amount for adjusting the conductivity period of said first electric discharge device and for rendering said second and third electric discharge devices sequentially conductive at predetermined times after said first electric discharge device becomes nonconducting.

8. Control apparatus comprising means including an electric discharge device for controlling the electrical energization of a load device so long as said electric discharge device is rendered conductive, means including a second electric discharge device for electrically energizing a second,

load device when said second electric discharge device is rendered conductive, means including a third electric discharge device for electrically deenergizing said second load device when said third electric discharge device is rendered conductive, means including a fourth electric discharge device for controlling the electrical energization of a third load device so long as said fourth electric discharge device is rendered conductive, each of said electric discharge devices being provided with a control element and a control circuit therefor, a condenser, means for charging and discharging said condenser and for producing a timing voltage which varies in magnitude with the lapse of time, means for initiating said t'ming voltage and simultaneously connecting it in each of said control circuits, means in each of said control circuits for applying to said control elements of said electric discharge devices bias voltages which are of increasingly greater magni. ude for said second, third, and fourth electric discharge devices from that applied to said control element of said first electric discharge device and which render said first and fourth electric discharge devices conductive and said second and third electric discharge devices nonconductive at the time said control circuits for said electric discharge devices are completed by the connection of said timing voltage in said control circuits, and means for simultaneously adjusting said bias voltages of said first, second and third electric discharge devices by the same amount for adjusting the conductivity period of'said first electric discharge device and for rendering said second and third electric discharge devices sequentially conductive at predetermined times after said first electric discharge device becomes nonconducting and before said fourth electric discharge device becomes nonconducting.

. JOHN M. FLUKE. 

